Re: [PATCH] refspec: allow @ on the left-hand side of refspecs

From: brian m. carlson <sandals@crustytoothpaste.net>
Date: Jul 30, 2018, 23:14 UTC
Message-ID: <20180730231451.GG945730@genre.crustytoothpaste.net>
In-Reply-To: <20180730175051.GA154732@google.com>

On Mon, Jul 30, 2018 at 10:50:51AM -0700, Brandon Williams wrote:

Show 18 quoted lines

> On 07/29, brian m. carlson wrote:
> > The object ID parsing machinery is aware of "@" as a synonym for "HEAD"
> > and this is documented accordingly in gitrevisions(7).  The push
> > documentation describes the source portion of a refspec as "any
> > arbitrary 'SHA-1 expression'"; however, "@" is not allowed on the
> > left-hand side of a refspec, since we attempt to check for it being a
> > valid ref name and fail (since it is not).
> > 
> > Teach the refspec machinery about this alias and silently substitute
> > "HEAD" when we see "@".  This handles the fact that HEAD is a symref and
> > preserves its special behavior.  We need not handle other arbitrary
> > object ID expressions (such as "@^") when pushing because the revision
> > machinery already handles that for us.
> 
> So this claims that using "@^" should work despite not accounting for it
> explicitly or am I misreading?  Unless I'm mistaken, it looks like we
> don't really support arbitrary rev syntax in refspecs since "HEAD^"
> doesn't work either.

Correct, it does indeed work, at least for me:

genre ok % git push castro HEAD^:refs/heads/temp
Total 0 (delta 0), reused 0 (delta 0)
To https://git.crustytoothpaste.net/git/bmc/git.git
 * [new branch]            HEAD^ -> temp

genre ok % git push castro @^:refs/heads/temp
Total 0 (delta 0), reused 0 (delta 0)
To https://git.crustytoothpaste.net/git/bmc/git.git
 * [new branch]            @^ -> temp

Note that in this case, I had to specify a full ref since it didn't exist on the remote and the left side wasn't a ref name.

Now it doesn't work for fetches, only pushes. Only the left side of a push refspec can be an arbitrary expression.

-- 
brian m. carlson: Houston, Texas, US
OpenPGP: https://keybase.io/bk2204